FINAL

Physics 101: Lecture 23

Temperature and Ideal Gas

 Today’s lecture will cover Textbook Chapter 13.1-13.4

Hour Exam 3 is Monday Nov. 17 Sign up for conflict exam by tomorrow!

Review Sun. night 8pm in Lincoln Hall Theatre Lectures covered: 14-21.

New practice problems for Chapt 8 posted in Lecture 16 Physics 101: Lecture 23, Pg 1

Internal Energy and Temperature

 All objects have “internal energy” (measured in Joules)  random motion of molecules » kinetic energy  collisions of molecules gives rise to pressure  Amount of internal energy depends on  temperature » related to average kinetic energy per molecule  how many molecules » mass  “specific heat” » related to how many different ways a molecule can move    translation rotation vibration » the more ways it can move, the higher the specific heat Physics 101: Lecture 23, Pg 2 10

Zeroth law of Thermodynamics

 If two objects are in thermo equilibrium with a third, then the two are in equilibrium with each other.

 If they are in equilibrium, they are at the same temperature Physics 101: Lecture 23, Pg 3 12

Temperature Scales

Farenheit 212 100 Celcius Kelvin 373.15

Water boils 32 0 273.15

Water freezes F  K  9 5 C C   32 C  5 9 273 C  K  F 32 273  NOTE: K=0 is “absolute zero”, meaning (almost) zero KE/molecule Physics 101: Lecture 23, Pg 4 14

Sick Act

You measure your body temperature with a thermometer calibrated in Kelvin. What do you hope the reading is (assuming you are not trying to fake some sort of illness) ? A. 307 K F  98.6

B. 310 K C. 313 K D. 317 K correct C  5 9 K  C ( F  32)  37 273  310 Physics 101: Lecture 23, Pg 5 17

Temp Scales ACT

 Two cups of coffee are heated to 100 degrees Fahrenheit. Cup 1 is then heated an additional 20 degrees Centigrade, cup 2 is heated an additional 20 Kelvin. Which cup of coffee is hotter?

A) One B) Two C) Same K  C  273 Physics 101: Lecture 23, Pg 6 20

Thermal Expansion

 When temperature rises  molecules have more kinetic energy » they are moving faster, on the average  consequently, things tend to expand  amount of expansion depends on…  change in temperature Temp: T  original length Temp: T+  T  coefficient of thermal expansion » L 0 » +  L = L 0  L =  L 0  + T  L 0  T (linear expansion) »  V =  V 0  T (volume expansion) L 0 Physics 101: Lecture 23, Pg 7  L 23

Density ACT

As you heat a block of aluminum from 0 C to 100 C its density A. Increases B. Decreases C. Stays the same CORRECT T = 0 C T = 100 C M, V 0 r 0 = M / V 0 M, V 100 r 100 = M / V 100 < r 0 Physics 101: Lecture 23, Pg 8 26

Differential Expansion ACT

 A bimetallic strip is made with aluminum  =16x10 -6 /K on the left, and iron  =12x10 -6 /K on the right. At room temperature, the lengths of metal are equal. If you heat the strips up, what will it look like?

A B C Aluminum gets longer, forces curve so its on outside Physics 101: Lecture 23, Pg 9 29

Swimming Preflight

Not being a great athlete, and having lots of money to spend, Gill Bates decides to keep the lake in his back yard at the exact temperature which will maximize the buoyant force on him when he swims. Which of the following would be the best choice?

1000.00

A. 0 C

999.95

B. 4 C C. 32 C D. 100 C E. 212 C CORRECT F B = r l Vg

999.90

999.85

999.80

999.75

999.70

999.65

999.60

999.55

Density 0 2 4 6 8 10

Water is most dense at 4 degrees C. so you're most likely to float in REALLY REALLY COLD, but not quite frozen, water. Kinda like Jack and Rose in Titanic. Unless he wants his skin to peel off...yeah, let's keep it at 32 C. Physics 101: Lecture 23, Pg 10 32

Tight Fit Preflight

An aluminum plate has a circular hole cut in it. An aluminum ball (solid sphere) has exactly the same diameter as the hole when both are at room temperature, and hence can just barely be pushed through it. If both the plate and the ball are now heated up to a few hundred degrees Celsius, how will the ball and the hole fit ? A. The ball won’t fit through the hole any more B. The ball will fit more easily through the hole C. Same as at room temperature CORRECT

35% 15% 50% 0% 10% 20% 30% 40% 50%

they are made out of the same material so they will expand the same when heated... its all Al dawg Physics 101: Lecture 23, Pg 11 35

Why does the hole get bigger when the plate expands ???

Imagine a plate made from 9 smaller pieces. Each piece expands. If you remove one piece, it will leave an “expanded hole” Object at temp T Same object at higer T: Plate and hole both get larger Physics 101: Lecture 23, Pg 12 36

Stuck Lid Act

A glass jar (  16x10 -6 K -1 = 3x10 -6 K -1 ) has a metal lid (  = ) which is stuck. If you heat them by placing them in hot water, the lid will be A. Easier to open B. Harder to open CORRECT C. Same Copper lid expands more, making a looser fit, and easier to open!

Physics 101: Lecture 23, Pg 13 38

Jar Act

A cylindrical glass container (  = 28x10 -6 k -1 ) is filled to the brim with water (  = 208x10 -6 k -1 ) . If the cup and water are heated 50C what will happen A) B) C) Some water overflows Same Water below rim Water expands more than container, so it overflows.

See example 13.3 in book Physics 101: Lecture 23, Pg 14 41

Molecular Picture of Gas

 Gas is made up of many individual molecules  Number density is number of molecules/volume N/V = r /m  r is the mass density  m is the mass for one molecule  Number of moles n=N / N A  N A = Avogadro’s number 6.022x10

23 mole -1 Physics 101: Lecture 23, Pg 15 43

Number Density ACT

 Two gas cylinders are filled such that they have the same mass of gas (in the same volume). One cylinder is filled with Helium, the other with Oxygen. Which container has the larger number density?

A) Helium B) Oxygen C) Same Helium molecule is “lighter” than Oxygen molecule. If you have the same mass, you must have many more Helium molecules than Oxygen. So the Helium number density is larger.

Physics 101: Lecture 23, Pg 16 46

Summary

 Temperature measure of average Kinetic Energy of molecules  Thermal Expansion   L =    V =  L 0  T (linear expansion) L 0  T (volume expansion)  Gas made up of molecules Physics 101: Lecture 23, Pg 17 50